Understanding the Second Harmonic Generation of Light from Nanometal Composites
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Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
The details for this synthesis are reported elsewhere.' Symmetric gold particles were prepared by depositing 0.3 C Au and 0.6 C Au over the 3.14 cm2 area for small and large particles, respectively. Additionally, for non-centrosymmetric particles, 0.1 C of Au was first deposited over the area, followed by another layer of Ag (0.1 C) and finally another layer of Au (0.2 C for small particles and 0.5 C for large particles). All of the composites were immersed in nitric acid (69-71 % EM), to dissolve any silver, leaving only gold in the pores. The composite films were rinsed with deionized water, ethanol, and acetone and air-dried. The procedure for preparing both types of particle composites is summarized in Figure 1. S2
3
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Figure 1. Schematic of nanoparticle synthesis:
(1) porous anodic alumina film after detachment from Al substrate; (2) one face of alumina film
4a
5a
coated with silver using plasma deposition; (3) electrodeposit silver foundation into pores; (4a) electrodeposit gold onto silver foundation to form (4b) particles; gold centrosymmetric electrodeposit layers of gold, silver, and then a second layer to form noncentrosymmetric gold particles; (5a and 5b) immerse film in nitric acid to remove silver foundation and silver spacing segments.
4b
S[
Sb
2] [
Nanoparticle Characterization Transmission electron microscopy was used to characterize the dimensions of the template synthesized gold nanoparticles. Additional sample preparation was required in order to obtain TEM (transmission electron microscope) images. The gold particle composite films were embedded in a resin and heated at 70 TC for 12 hours. A 70 ýim section was cut using a diamond knife (SPI Inc.) and placed on a Formuvar-coated Cu grid (200 mesh, EM Sciences). The samples were then examined with a JEOL 1200 EX transmission electron microscope. Linear Optical Analysis The linear polarization analysis of the composite films was performed using a Hitachi U 3501 spectrophotometer equipped with a 210-2130 polarizer accessory. Extinction spectra were obtained between X = 350 nm and X = 800 nm at normal incidence (defined as 0 = 00, and corresponding to the case where the incident electric field is perpendicular to the pore axes), and at incidence angles 0 = 20', 300, and 45', under p-polarization (the incident electric field polarized parallel to the plane of incidence). A schematic of the sample/polarizer configuration is shown in Figure 2.
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.
polarizer
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.
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Figure
sample
j-Ir, ..
2.
Schematic
of
polarzation
spectroscopy setup. The sample film is rotated
t
. .e0to
detector
about an axis perpendicular to the page.
The angle of incidence is indicated by 6. p-
"Polarizationcorresponds
Soriented
gold
to an incident electric field in the plane of the page. s-Polarization corresponds to an electric field oscillating perpendicular to the page.
particles
Second Harmonic GenerationStudies The SHG studies employed a high repet
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